Process for the separation of platinum group metals

ABSTRACT

Disclosed herein is a process for the separation and recovery of Rhodium values from aqueous mineral acid solutions also containing Iridium and/or Ruthenium which comprises contacting the metal bearing aqueous solution with a water immiscible organic solvent containing an organically substituted quaternary amine salt to extract Iridium and Ruthenium into the solvent phase leaving Rhodium in the aqueous raffinate. The loaded organic phase is stripped of Iridium and Ruthenium in two sequential steps by contacting it first with an alkaline solution then redissolving the resulting precipitate in an acidified reducing solution.

This invention relates to a method for separating dissolved metal saltsfrom aqueous mineral acid solutions and more specifically to a schemefor separating Rhodium from Iridium and/or Ruthenium by solventextraction with an organically substituted quaternary ammonium salt andrecovering the Iridium and Ruthenium values from the loaded organic.Still more specifically, the invention relates to a method for theorganic solvent extraction of Iridium and/or Ruthenium from aqueouschloride solutions containing Rhodium, Iridium and Ruthenium andrecovery of the isolated Iridium and Ruthenium values from the loadedorganic phase.

The separation of Rhodium from Iridium has long been considered adifficult aspect of Platinum group metal separation. The traditionalmethods for separating Rhodium-Iridium-Ruthenium from one another arewell known in the art, but involve long and tedious processingoperations.

More recently, somewhat faster methods have been evolved for separatingIridium-Rhodium-Ruthenium from aqueous solution by ion exchange. Thereare, however, several drawbacks and disadvantages involved in suchprocesses. Ruthenium may be reduced on ion exchange resins and the IrCl₆-2 ion is difficult to elute. Also, the nature of the Rhodium-containingspecies is very sensitive to solution conditions on the resin column andmay change when the metal bearing solution is on the column to preventthe separation.

Tertipis et al. describe the solvent extraction of Iridium fromhydrochloric acid solutions containing Rhodium through the use oftributyl phosphate in Analytical Chemistry 33 (1961), No. 12, pages 1650through 1652. However, this technique is undesirable since it involvesreaction conditions which significantly restrict its general usefulness.

The problem of successfully separating Rhodium from Iridium by solventextraction with tributyl phosphate is further complicated when thepregnant aqueous solution in which the metals are dissolved alsocontains Ruthenium. In such instances substantial difficulty isencountered in obtaining a pure Rhodium product as the Rutheniumcontaminates both the Iridium and Rhodium thereby frustrating theisolation of a pure form of either metal.

It has now been unexpectedly discovered that Rhodium values can bequickly and easily separated from aqueous mineral acid solutionscontaining Rhodium, Iridium and Ruthenium by solvent extraction with anorganic solvent containing an organically substituted quaternaryammonium compound. It has also been found that the Iridium-Rutheniumvalues extracted into the amine solvent can be stripped and recovered asa mixture of Iridium and Ruthenium salts by sequentially contacting theloaded organic with an aqueous alkaline solution and an acidifiedreducing agent. In operation, a water immiscible organic solventcontaining an organically substituted quaternary ammonium salt isbrought into contact with the aqueous mineral acid solution and forms acomplex with iridium and Ruthenium which are present in the solution intheir anionic states. The complex is extracted into the solvent phaseleaving Rhodium (present in the acid solution as a cation) in theaqueous raffinate phase. After phase separation, Iridium and Rutheniumare simultaneously stripped and recovered from the loaded organic bysequential contact with predetermined stoichiometric quantities of analkaline solution and an acidified reducing solution.

It is accordingly an object of the present invention to provide a highlyselective process for separating Rhodium from aqueous solutionscontaining Iridium, Rhodium and Ruthenium.

Another aspect of the invention is a method for separating Rhodium froman aqueous solution also containing Ruthenium and Iridium by extractingthe Iridium and Ruthenium into an organic phase containing a substitutedquaternary ammonium compound.

A further aspect of the present invention involves the method ofstripping and recovering the Iridium and Ruthenium complex from theloaded amine organic phase by sequential treatment with predeterminedstoichiometric quantities of an alkaline solution and an acidifiedreductant stripping solution.

These and other aspects of the present invention are more completelyexplained in the following specification and examples.

According to the present invention, cationic Rhodium is separated froman aqueous mineral acid solution containing cationic salts of Rhodium aswell as Iridium And Ruthenium in their anionic oxidized state by solventextraction with an organically substituted quaternary ammonium salt.Contacting the aqueous solution with a solvent containing the quaternaryamine leads the Iridium and Ruthenium values to form a complex with theamine that is preferentially soluble in the solvent phase, leavingRhodium in the aqueous raffinate. As used in the present invention, theterm "raffinate" refers to an aqueous solution (or phase) after solventextraction, i.e., a solution that has been depleted of all or part ofits valuable metal content by transfer to an organic phase.

The Rhodium, which must be present in the mineral acid solution in itscationic state, is not extracted into the amine solvent, and is won fromthe aqueous raffinate by conventional processes such as coppercementation. The Iridium-Ruthenium loaded organic amine phase is treatedwith at least the stoichiometric quantity of an aqueous solution of analkaline reagent required to breakup the amine complex formed betweenIridium and Ruthenium and produce a precipitate which is the alkalinesalt form of the extracted metal values. The resulting alkaline/solventmixture is then contacted with an acidified reducing agent to solubilizethe Iridium and Ruthenium precipitates into an aqueous acidic solutionfrom which they may readily be isolated by known methods.

The aqueous phase from which Iridium and Ruthenium are extracted in thepresent invention is ordinarily a mineral acid leach solution of thetype normally resulting from the fusion and leaching of Platinum metalore concentrates. The invention will be further described by referenceto separation and recovery of Rhodium, Iridium and Ruthenium fromhydrochloric acid solutions such as generally occur in Platinum groupmetal recovery. However, the invention is not limited as such and may beoperated to separate metals from solutions of other mineral acids whichare used in the recovery or assay of Platinum group metal values,provided the acid does not attack or degrade the organic extractant andwill afford the formation of organic soluble complexes of the desiredmetals with the quaternary amine extractant. In aqueous chloridesolutions, the soluble Rhodium-Iridium-Ruthenium compounds are generallypresent as complex chloro salts or in a form of their correspondinghydrochloric acid complexes. Typically, such leach solutions result fromcrude ore processing operations and range between 0.1 to about 5 normalHCl and up to about 250 grams per liter CL⁻ and in some instanceshigher. In addition to the Platinum group metals, the solutions maycontain other base metal impurities such as lead, copper, bismuth,nickel, aluminum, silica, silver, and barium.

It has been discovered that in order to achieve an effective separationof Iridium and Ruthenium from Rhodium in the preferred hydrochloric acidsolutions, it is necessary to have Rhodium present in the form of acationic chloro complex of Rhodium and for the Iridium and Ruthenium toexist as oxidized Iridium and Ruthenium chloro complexes respectively.This is important as the oxidized Iridium and Ruthenium chloro complexesbehave as an anion toward the organic extraction mixture and areextracted, whereas the Rhodium chloro complex behaves as a cation and isnot extractable with the organically substituted quaternary amineextraction agent. The foregoing differences in ionic condition aremaintained throughout the extraction so that the organic phasecontaining the amine complexing agent does not become fouled withRhodium chloro complexes which would behave as anionic species and beextracted. The aqueous acid solutions from which the aforementionedmetals are extracted are preferably substantially free of gold, iron,Platinum, and Palladium which are removed beforehand by conventionaltechniques well known in the art.

The extraction liquid used to separate Iridium and/or Ruthenium fromRhodium consists of three constituents: an organic extractant, a waterimmiscible carrier solvent and a phase modifier.

In the present invention an aqueous mineral acid solution containing,for example, Iridium, Rhodium and Ruthenium dissolved in a hydrochloricacid solution is contacted with a water immiscible organic solventcontaining a quaternary ammonium compound capable of forming complexeswith Iridium and Ruthenium that are preferentially soluble in theresultant organic phase. The quaternary ammonium compounds capable ofperforming these functions have the following basic structure: ##STR1##

Wherein R₁, R₂, R₃ and R₄ are straight or branched aliphatic alkyl oraromatic hydrocarbon groups. Generally at least one of R₁, R₂, R₃ and R₄are fatty alkyl groups. Aliquat 336, methyl tricaprylyl ammoniumchloride, manufactured by General Mills, is an effective extractant andhas the following cation: ##STR2##

wherein R₁, R₂, and R₃ are hydrocarbon chains having eight to ten carbonatoms, with eight carbon atoms prevailing. Also useful as the aminesolvent extractant are Adogen 468 methyltri-n-alkylammonium chloride(average C₁₀), and Adogen 464 methyltri-n-alkylammonium chloride (C₈-C₁₀) (both made by Ashland Chemical Co.). The organically substitutedquaternary amines which may be used in the present invention must besufficiently soluble in at least one of the solvents referred to below,or mixtures of them to make at least a 1% solution. Finally, theammonium compound should provide for ready phase disengagement followingextraction. The preferred organic extractant in the present invention isAliquat-336. Prior to use in the extraction the amine extractant isusually conditioned to the form of the acid solution to be contacted.Thus in the preferred embodiment in which Iridium and Ruthenium areextracted from hydrochloric acid solution, the extractant is conditionedto chloride form by treatment with NaCl in 1N HCl.

The major constituent of the extraction liquid is a water immisciblecarrier solvent in which the organic amine extractant is dissolved toform the organic phase.

Conventional organic solvents including, for example, aliphatichydrocarbons such as petroleum derived liquid hydrocarbons, eitherstraight chain or branched, kerosene, fuel oil, etc., are useful in theinvention. Various aromatic solvents or chlorinated aliphatic solventsmay also be employed such as benzene, toluene, xylene, carbontetrachloride and perchloroethylene. The organic solvents must besubstantially water immiscible and capable of dissolving the organicallysubstituted amine extractant. In addition, the solvent should be inertand not interfere with the extraction of Iridium and Ruthenium metalvalues from acid solution by the organically substituted amine. Keroseneavailable as AMSCO 175 is preferably employed because of its readyavailability and as a matter of economy.

The organically substituted quaternary amine component of the organicextractant mixture must have a solubility of at least about 1% by weightin the hydrocarbon solvent of the organic phase which must be insolublein water.

A phase modifier is also admixed with the carrier solvent and extractantto prevent the formation of a third phase in stripping the pregnantorganic. Water insoluble straight or branched chain aliphatic alcoholscontaining at least 6 carbon atoms are generally used as phasemodifiers. Examples of suitable phase modifiers include isodecanol,2-ethyl hexanol and tridecanol. Isodecanol is preferred for use in thepresent invention.

The organic mixtures of the present invention will usually contain fromabout 5 to 15 volume percent (%) of the organic amine extractant,between about 85 and 95 volume percent (%) of the carrier solvent, andfrom about 1 to about 5 volume percent (%) of the phase modifier.Although the preceding criteria are generally applicable, the inventionis not limited to operation within these boundaries. Since only alimited amount of the active extracting ingredient is present in thesolvent phase, it can only hold a limited amount of any given metallicelement at saturation. Once the concentration of metal in the solventhas reached the saturation level, no additional metal will go into thesolvent regardless of its concentration in the aqueous phase. Thequantity of metal which is given solvent extractant will hold is termed"the maximum loading " and governs the total quantity of solventrequired to do a given amount of extraction. Based upon the maximumloading characteristics of the particular extractant, the metal-bearingcharacteristics of the leach liquor that is to be extracted and thenumber of extraction stages to be employed, the concentration ofextractant and phase modifier in the solvent may be adjusted, or theOrganic/Aqueous (O/A) ratio for any particular extractant concentrationmay be varied to achieve a desired loading. In one effective version ofthe extraction process the organic liquid mixture used to extractIridium and Ruthenium from an aqueous hydrochloric acid solutioncomprises 10 volume percent (%) Aliquat-336, 87 volume percent (%)kerosene and 3 volume percent (%) isodecanol. As a measure of economy,it is preferred to employ the lowest organic/aqueous ratio that willprovide efficient separation of the desired metal values from a givenaqueous mineral acid solution.

The liquid-liquid extraction may be carried out by continuouscountercurrent or batch processing procedures.

Typical apparatus for use in the present invention could include(without limitation thereto) a multiple stage countercurrentmixer-settler system in which the barren organic solvent and a pregnantaqueous stream are mixed together for a predetermined time periodfollowing which they are permitted to separate in a settling reservoir.The solvent and aqueous then flow in opposite directions to the nextstage of contact.

Briefly summarizing the separation and recovery process operation, freshmetal bearing aqueous mineral acid solution is contacted and admixedwith the organically substituted quaternary amine solvent for apredetermined time period under oxidizing conditions. The iridium andruthenium anions in the aqueous solution form a complex with the amineand are extracted into the solvent phase. The admixture is permitted tosettle into distinct organic and aqueous phases which are isolated fromone another. Iridium and ruthenium are simultaneously stripped from themetal loaded organic phase by sequential treatment with at least thestoichiometric quantity of alkaline solution which will neutralize theacid salt of the amine followed by treatment with an acidic reducingsolution. Rhodium is won from the aqueous raffinate by known methods(e.g., cementation with copper powder). Iridium and ruthenium may alsobe isolated from the stripping solution using conventional techniquesknown to the art.

An important aspect of the present invention involves conditioning(oxidizing) the metal bearing acid solution to an emf or redox potentialas measured by means of a platinum-calomel electrode of between about-500 and -1000 millivolts (otimally about -900 mv) prior to the organicextracting operation in order to maintain high extraction efficienciesand promote the production of rhodium solutions essentially barren ofiridium and ruthenium. It should be noted that while the extractionprocess will operate at emf values less than -500 mv, extractionefficiencies become correspondingly lower. The conditioning treatment iscontinued through the extraction to insure that the aqueous phase ismaintained in the oxidized state. The conditioning operation can beaccomplished by the addition of sodium hypochlorite (NaOCl) solution ata controlled rate to the aqueous acid solution to be extracted tomaintain the solution in an oxidized condition (indicated by obtainingan emf reading between -500 and -1000 millivolts, and preferably about-900 mv). Alternatively, chlorine gas (Cl₂) or other oxidants (e.g.,peroxide) can be employed to accomplish the same results as sodiumhypochlorite.

The iridium-ruthenium extraction and stripping operations are preferablycarried out at about 25° C although satisfactory performance has beenachieved at temperatures in the range 20° -40° C and up to 50° C andhigher. At temperatures below about 20° C the phase disengagement isslow, while operation above 40° C is hazardous due to the danger offire.

Alkaline stripping reagents for use in the present invention must bewater soluble compounds which will convert the extracted metal valuescontained in the organic solvent into reaction products that are readilysoluble when contacted with the acidic reduction solution. Strippingefficiency (i.e., the ability to remove a large quantity of metal saltper unit volume of strippant) is also an important criteria forselection of an alkaline stripping agent. Suitable alkaline strippingagents include water soluble alkali and alkaline earth carbonates,bicarbonates and hydroxides, e.g., sodium and potassium hydroxide,carbonate or bicarbonate, although sodium hydroxide is perferablyemployed. The amount of alkaline strippant required is at least thequantity which will neutralize the acid salt (usually the chloride) formof the quaternary amine organic and desirably includes in excess of thestoichiometric amount (preferably about 50-100%) of the alkaline agentto insure efficient stripping within the shortest possible contacttimes. By contacting the loaded organic solvent with the alkalinestripping solution, the organic soluble Iridium and Ruthenium organicamine complexes are converted to metal salts and chloride form of theamine.

Although metallic values can be recovered from the loaded organic usingonly the acidified reducing strip solution and without a prior contactwith an alkaline reagent, it has been unexpectedly discovered that aconsistently higher percentage of the Iridium and Ruthenium metalspresent in the organic solvent were stripped using sequential treatmentwith alkaline solution and an acidic reducing agent.

The acidified reductant stripping agents are selected based upon theircapacity to contribute additional stripping action to the alkalinetreated loaded amine organic as well as for their ability to maintain areducing environment in the strip solution. The latter criteria is mostimportant to prevent inadvertent reextraction of the Platinum groupmetal values from the strip solution. Also, the strippant should notcontribute any foreign metals to the organic which might cause eventualfouling or a reduction in loading capacity. Satisfactory reductantstripping agents include acidic solutions of hydrazine salts,hydroxylamine salts, SO₂, and conventional organic reducing agents(i.e., organic acids such as oxalic). The reductant stripping solutionsare acidified to between about 0.5-2.5 N (preferably 2.0 N) tosolubilize the Iridium and Ruthenium alkaline salts. One suitablereducing solution is hydrazine dihydrochloride (N₂ H₄ .2HCl) acidifiedto 2.0 N HCl.

The quantity of acidified reducing agent utilized is at least thestoichiometric amount based upon the alkaline strippant previouslyadded, and desirably includes in excess of the stoichiometric amount(preferably about 100-150%) to insure complete dissolution of theprecipitated Iridium and Ruthenium values in the aqueous phase.Additionally, some further stripping action is realized during thecontact period with the acidified reducing strip solution. Althoughsuggested concentrations of strippant solutions have been describedherein, those skilled in the art will recognize that these may be varieddepending upon the organic volumes to be treated, stripping efficiencyof a particular strippant, to adjust the quantity and concentration ofstrip to yield strip solutions containing significant quantities ofdissolved Iridium and Ruthenium values and to avoid dilution andhandling of weak and/or large volumes of solution.

The time required for stripping contact will vary from one loadedorganic to another depending upon the particular solvent system, thequantity of Iridium and Ruthenium sought to be stripped and thetemperature at which the stripping operation is conducted. In mostinstances strip contact times of between 1 and 10 minutes can beutilized to provide satisfactory results.

The invention is further illustrated by the following examples.

The examples present in Table 1 were performed to illustrate the methodof effecting a more complete separation of Rhodium from Iridium andRuthenium by maintaining a high oxidation state of the aqueous feedliquor. It should be noted, however, that the present invention is notlimited to operation strictly according to the instant example.

In Test No. 1 a predetermined amount of Iridium-Rhodium-Rutheniumaqueous acid solution analyzing 4.6 g/l Rhodium, 1.25 g/l Iridium and4.5 g/l Ruthenium, 265 g/l Cl⁻ at 1 normal HCl and having a measured emfof -520 millivolts was contacted four times in succession with freshorganic extractant at an organic to aqueous ratio of 2 to 1. Eachcontact was for a period of 2 minutes. Following each contact the phaseswere separated and the amount of Iridium and Ruthenium extracteddetermined by analysis. In Test No. 2 the identicalRhodium-Iridium-Ruthenium solution was adjusted to emf -900 millivoltsby gaseous Cl₂ oxidation and then extracted 4 times in succession withfresh solvent in a like manner described above. The extraction organicin both of the above examples contained 10 volume % Aliquat-336, 3volume % isodecanol, and 87 volume % kerosene (AMSCO 175) and wasconditioned to the chloride form of the organic by contacting with asolution of 100 g/l NaCl in 1 normal HCl followed by washing using asolution 20 g/l NaCl adjusted to pH 1.5 with HCl.

                                      Table 1                                     __________________________________________________________________________    Rh-Ir-Ru Extraction by Aliquat-336 at Various Solution EMF's                  Assay g/1                                                                     Test                                                                              Contact                                                                            Aqueous                                                                              Feed Aqueous                                                                              Raffinate   Loaded Organic                                                                              % Extracted             No. No.  EMF, mv                                                                              Rh  Ir  Ru  Rh  Ir  Ru  Rh  Ir   Ru   Rh Ir Ru                __________________________________________________________________________    1        -520   4.6 1.25                                                                              4.5                                                       1                       4.3 0.43                                                                              1.8 0.06                                                                              0.30 1.4                              2                       4.1 0.34                                                                              1.3 0.08                                                                              0.05 0.23                             3                       3.9 0.31                                                                              1.1 0.09                                                                              0.03 0.09                             4                       3.7 0.27                                                                              0.8 0.09                                                                              0.03 0.08 20 78 82                2        -900   4.6 1.25                                                                              4.5                                                       1                       4.4 0.02                                                                              0.7 0.04                                                                              0.54 2.0                              2                       4.1 0.03                                                                              0.1 0.07                                                                              0.02 0.27                             3                       3.9 0.03                                                                               0.02                                                                             0.08                                                                              0.01 0.04                             4                       3.8 0.03                                                                              0.008                                                                             0.06                                                                              <0.01                                                                               0.009                                                                             17 97 99                __________________________________________________________________________

It will be seen from the above results that maintenance of a highoxidation state during extraction results in a more complete separationof Iridium-Ruthenium from Rhodium and produces a lower Iridium/Rutheniumraffinate for recovery of Rhodium by cementation.

The examples presented in Table 2 were performed to show the increase instripping efficiency when using the combination alkaline plus acidifiedreducing solution strip treatment. For both examples in Table 2 a 10% byvolume Aliquat-336 solution in kerosene containing 3% by volumeisodecanol was loaded with Iridium and Ruthenium by contacting with anacidic Rhodium-Iridium-Ruthenium chloride solution oxidized to emf -900mv by addition of 50 g/l NaOCl solution. A 100 ml portion of the loadedorganic was agitated for 10 minutes with 50 g/l N₂ H₄.2HCl in 2 N HCl atan organic to aqueous ratio of 2 to 1 at room temperature. Thepercentage of Iridium and Ruthenium stripped was determined by analysisof the separated phases. A second 100 ml portion of the same loadedsolvent was agitated with 8 ml of 200 g/l NaOH (2X stoichiometric basedon the normality of the prepared amine organic) for 5 minutes at roomtemperature. Following the caustic reaction period, 42 ml of 50 g/l N₂H₄.2HCl in 2 N HCl was added (2.1 X stoichiometric based on the amountof caustic solution added) and the mixture stirred for an additional 10minutes at room temperature. The final stripped volumes so obtained hadan organic to aqueous ratio of 2/1. As in the first test, the percentageof Iridium and Ruthenium stripped was determined by analysis of theseparated phases.

                                      Table 2                                     __________________________________________________________________________    % of Iridium-Ruthenium Stripped                                                          Organic Assay g/l       Assay g/l                                  Test       Loaded      Stripped    Strip Solution                                                                            % Stripped                     No.                                                                              Strippant                                                                             Rh  Ir  Ru  Rh  Ir  Ru  Rh  Ir  Ru  Rh Ir Ru                       __________________________________________________________________________    1  N.sub.2 H.sub.4 . 2HCl                                                                0.030                                                                             0.32                                                                              0.59                                                                              0.020                                                                             0.18                                                                              0.49                                                                              0.020                                                                             0.28                                                                              0.21                                                                              33 44 17                          in 2N HCl                                                                  2  NaOH plus                                                                             0.030                                                                             0.32                                                                              0.59                                                                              0.008                                                                             0.04                                                                              0.08                                                                              0.044                                                                             0.56                                                                              0.97                                                                              73 88 86                          N.sub.2 H.sub.4 . 2 HCl                                                       in 2N HCl                                                                  __________________________________________________________________________

It can be seen from the above table that the alkaline plus acidifiedreductant strip system significantly increases the percentage recoveryof Iridium and Ruthenium from the loaded solvent. The beneficial resultobtained from the two-step stripping system is the production of goodbarren organic for recycle back to the extraction stages of the Rhodiumseparation circuit.

From the foregoing it will be seen that the present invention combines arapid technique for separation of Iridium and/or Ruthenium from Rhodiumwith an efficient extraction and stripping system. The separation andrecovery procedure are quite specific and will function in solutionscontaining widely varying quantities of the respective metals. Theeconomy and speed of operation of the present process make it ideal forincorporation as part of a continuous processing system for separationof Rhodium essentially free of Iridium and/or Ruthenium from aqueousacid solutions of such metals.

What is claimed is:
 1. A process for the separation and selectiverecovery of Rhodium, and/or Ruthenium and Iridium values from an aqueousacidic medium which comprises:contacting the medium with an organicextraction reagent comprising a water immiscible solvent havingdissolved therein an organically substituted quaternary ammoniumcompound having the structure ##STR3##wherein R₁, R₂, R₃ and R₄ arehydrocarbon groups, said compound being sufficiently soluble in saidsolvent to make a 1% solution and capable of forming complexes withIridium and Ruthenium that are preferentially soluble in said solventand whereby said contacting results in the formation of an organicextract phase and an aqueous raffinate phase, maintaining said medium atan emf between about -500 and -1000 mv during said contacting operation,separating said organic extract phase from said aqueous raffinate phase,contacting said organic extract phase with at least the stoichiometricquantity of an aqueous alkaline stripping agent required forneutralization of the organic extract phase, said contact resulting inthe formation of an aqueous phase loaded with Iridium and Ruthenium anda stripped organic phase, and contacting said stripped organic phase andsaid loaded aqueous phase with a solution consisting of an acidifiedreducing agent which is at least the stoichiometric equivalent of saidalkaline agent.
 2. The process of claim 1 wherein at least one of R₁,R₂, R₃ and R₄ is a fatty alkyl group.
 3. The process according to claim2 which comprises introducing an oxidant into said aqueous medium tomaintain said medium at an emf between about -500 and about -1000millivolts during said contacting operation.
 4. The process of claim 3which comprises conducting said contacting operation at a temperaturebetween about 20° and 40° C.
 5. The process according to claim 3 whereinsaid oxidant is sodium hypochlorite.
 6. The process of claim 2 whereinsaid aqueous acidic medium is hydrochloric acid.
 7. The process of claim3 which comprises adding copper powder to said separated aqueousraffinate phase to recover Rhodium.
 8. The process of claim 2 whereinsaid alkaline stripping agent is a water soluble member selected fromthe group consisting of the carbonates, bicarbonates and hydroxides ofalkali and alkaline earth metals whereby said contact results in theformation of an Iridium and Ruthenium loaded aqueous phase and astripped organic phase.
 9. The process of claim 1 which comprisescontacting said loaded aqueous phase and said stripped organic phasewith a sufficient quantity of said acidified reducing agent solution tomaintain the emf of said loaded aqueous phase below about -600millivolts.
 10. The process of claim 9 wherein said reductant strippingagent is a member selected from the group consisting of acidifiedsolutions of hydrazine salts, hydroxyl amine salts, reduced metallicsalts, SO₂, and organic dicarboxylic acids.
 11. The process of claim 10wherein said acidified reductant is hydrazine dihydrochloride of theformula N₂ H₄.2HCl.
 12. The process of claim 11 which comprisescontacting the stripped organic phase with an aqueous mineral acidfollowing treatment with said acidified reducing agent to removeentrained metal values and subsequently reusing the organic phase toextract a fresh metal containing acidic medium.
 13. A continuous processfor the separation and recovery of Rhodium dissolved in aqueous chloridesolutions with Iridium which comprises:contacting said aqueous chloridesolution with an organic solvent containing at least 1% by weight of anorganically substituted quaternary ammonium halide having the followingstructure: ##STR4## wherein R₁, R₂, R₃ and R₄ are hydrocarbon groups fora predetermined time period to form an organic extract phase and anaqueous raffinate phase, maintaining said Iridium and Rhodium containingaqueous chloride solution at an emf between about -500 and -1000millivolts during said contacting operation, separating said extractphase from said aqueous phase, contacting said separated extract phasewith at least the stoichiometric amount of aqueous sodium hydroxidesolution required to neutralize the chloride form of said amine and forma metallic hydroxide precipitate, said contact resulting in formation ofa treated extract phase and a treated aqueous phase, contacting saidtreated extract phase and said treated aqueous phase with at least astoichiometric amount based on the stoichiometric value of said sodiumhydroxide solution of an acidified aqueous reducing agent, said contactresulting in the formation of a loaded aqueous phase and a strippedorganic phase, separating said loaded aqueous phase and said strippedorganic phase, and recovering Iridium from said loaded aqueous phase.